Heatable hoses with flexible hose walls are widely used. They are mainly applied as respiration hoses, for example for medical purposes or for pulmonary automatic devices for diving or for rescue purposes. The hoses are manufactured with as thin a hose wall as possible, in order to be as flexible and lightweight as possible. Respiration hoses are, as a rule, heatable, to prevent condensation of the humidity accumulating in the hose. The presence of humidity in a respiration hose is inevitable if the respiration air supplied to a patient has to be humidified. Excessive condensed humidity in the respiration hose may lead to both hygienic and technical problems. In particular, during respiration, no water must get into the patient's lungs. If the heating of the hose and, thus, the heating temperature is controlled by temperature-measuring arrangements inside the hose, these measured values may be adulterated through the presence of (water) condensate. To completely avoid the condensation of humidity, as uniform a heating as possible over the entire length of the hose is desirable.
Different embodiments of heatable hoses are known, in which the hose is usually heated by means of heating wires (resistance wires). The heating wires can be arranged both inside and outside the hose wall. The hose wall can be surrounded, for example, by a helicoidal outer support bead, also called “reinforcing rib”, a pair of electric conductors or a pair of heating wires being carried in the support bead or between support bead and hose wall. The two heating wires can be connected with each other on one end of the hose in an electrically conductive manner, to bring about a closed heating-current circuit, while the other two ends of the heating wires are led out of the support bead on the other end of the hose and can be connected to the poles of a voltage source or a heating-current source. The current flowing in this way through the heating wires heats the heating wires, which, in turn, heat the hose and the medium flowing therein. Such a hose is known, for example, from DE 695 27 528 T2.
Due to the spatial proximity of the heating wires arranged in the helicoidal support bead or the reinforcing spiral, a contact of the two electric conductors or heating wires and, thus, a short circuit might occur. As the reinforcing spiral strengthening the hose wall has to guarantee a high flexibility of the hose, a suitable dimensioning of the reinforcing spiral results, of course, in spatial proximity of the two heating wires.